JP2007172854A - Method of manufacturing foamed insulated wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a foamed insulated wire which is coated by a foamed insulator with less surface unevenness and outside diameter variation by using a thermoplastic resin compound in a dried condition, on which a porous body is added as a foaming nucleating agent. <P>SOLUTION: The method of manufacturing the foamed insulated wire supplies the thermoplastic resin compound in the dried condition, on which the porous body such as zeolite, silica, activated carbon, or silica gel is added as the foaming nucleating agent, to an extruder, extrudes the foamed insulator outward of a conductor by continuously injecting foamed gas to the extruder by a gas injection part provided with a gas pressure control means 20. Thereby, the injected foamed gas is effectively adsorbed to the porous body and is dispersed, and thus a huge foaming cell is not likely to be formed, and the wire of the excellent foamed insulator with the less surface unevenness (surface roughness) and outside diameter variation enabling to provide fine foam is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a foam insulated wire coated with an excellent foam insulator with less surface irregularities and outer diameter fluctuations.

In the case of insulated wires used in various electronic devices in recent years, for example, in a high-frequency coaxial cable, the used frequency band has reached the GHz order. In the GHz band, a cable characteristic having a smaller attenuation than that in the low frequency band is required. Therefore, foaming is performed on the insulator coated on the inner conductor (center conductor) (patent) Literatures 1-2).
Japanese Patent No. 3227091 Japanese Patent No. 2668198

  As the insulator, in addition to polyethylene resin, thermoplastic fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) are also used. It is used.

For foaming such insulators, chemical foaming is performed by filling the resin compound with a chemical substance that is foamed by heating during extrusion, or nitrogen gas or carbon dioxide gas is introduced into the resin compound from the outside during extrusion. The physical foaming method is used.
However, it is difficult to obtain a uniform and fine foam insulator with a high foaming degree only by these methods.

  For this reason, it has been proposed that a foaming nucleus, that is, a foaming nucleating agent is added in advance to the resin compound to promote foaming. For example, it is known to use boron nitride (BN) as a foam nucleating agent in the physical foaming method. In the case of boron nitride, it is thermally stable near the extrusion temperature of the thermoplastic fluorine-based resin, has low reactivity, and exhibits excellent dielectric properties.

However, foaming by using boron nitride has limitations in terms of increasing the degree of foaming. Therefore, it is possible to improve the foaming degree by adding an inorganic metal salt in addition to boron nitride, or to make the foaming degree finer. Attempts have been made (Patent Document 3).
Japanese Patent Laid-Open No. 01-172431

Under such circumstances, the present inventor conducted various tests and found that the thermoplastic resin compound added with the porous material as a foam nucleating agent was supplied in a dry state to the extruder, and the extruder was supplied. In the case where the foaming gas is continuously injected by the gas injection part equipped with the gas pressure control means and the foamed insulator is pushed out of the conductor, the injected foamed gas is effectively adsorbed by the porous body and dispersed. Therefore, it has been found that it is difficult to form a huge foam cell, the foam can be made finer, and an excellent foamed insulator electric wire with less surface irregularities (surface roughness) and outer diameter fluctuation can be obtained.
In particular, as the base resin of the thermoplastic resin compound, a thermoplastic fluorine-based resin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is used. While adding the zeolite or silica of the porous body to be used in a specific size range and a specific mass% range, the compounded material is handled in a sufficiently dry state, and further, a foaming gas (nitrogen gas or It has been found that a more stable supply of carbon dioxide etc. is even more effective.

  The present invention has been made in view of this point of view, and provides a method for producing a foam insulated wire in which a specific porous body is added as a foam nucleating agent to a base resin, and a foam insulation having excellent characteristics is coated. To do.

  According to the first aspect of the present invention, a thermoplastic resin compound added with a porous material as a foam nucleating agent is supplied in a dry state to an extruder, and the extruder is provided with a gas having a gas pressure control means. In the method for producing a foam insulated wire, the foam insulation is continuously injected by an injection portion and the foam insulation is pushed out of the conductor.

  In the second aspect of the present invention, the base resin of the thermoplastic resin compound is a thermoplastic fluororesin such as a tetrafluoroethylene-hexafluoropropylene copolymer or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. It exists in the manufacturing method of the foam insulated wire of Claim 1 characterized by the above-mentioned.

  A third aspect of the present invention is the method for producing a foam insulated wire according to the first or second aspect, wherein the porous body is zeolite, silica, activated carbon, or silica gel.

  The present invention according to claim 4 is characterized in that the porous body is zeolite having a median diameter of 1 to 10 μm, and 0.1 to 1% by mass is added to the base resin of the thermoplastic resin compound. It exists in the manufacturing method of the foam insulated wire of 1 or 2.

  The present invention according to claim 5 is characterized in that the porous body is silica having a median diameter of 1 to 10 μm, and 0.2 to 1.5 mass% is added to the base resin of the thermoplastic resin compound. It exists in the manufacturing method of the foam insulated wire of Claim 1 or 2.

  According to a sixth aspect of the present invention, there is provided an external storage part in which the thermoplastic resin compound in the dry state is stored, a compound transport pipe connected from the external storage part to a hopper of the extruder, and a hopper of the extruder 6. The method for producing a foam insulated wire according to claim 1, wherein the dried thermoplastic resin compound is supplied to an extruder.

  The present invention according to claim 7 is the method for producing a foam insulated wire according to claim 1, wherein the hopper of the extruder is a hopper with a drying section. .

  The present invention according to claim 8 is characterized in that the gas pressure control means of the gas injection section comprises an air compressor and a gas booster with a built-in buffer tank. Or it exists in the manufacturing method of the foam insulated wire of 7 description.

  According to the manufacturing method of the foam insulated wire of the present invention, the injected foam gas is effectively adsorbed by the porous body and dispersed in the thermoplastic resin compound by the above configuration. And since this porous body functions as a foam nucleating agent, a phenomenon such as rapid foaming, so-called bumping, is suppressed, and stable foaming is obtained. Further, high injection efficiency of the foaming gas can be obtained. As a result, it is difficult to form a huge foam cell, and it is possible to obtain a foamed insulating wire that can be finely foamed and has less surface irregularities (surface roughness) and fluctuations in outer diameter.

  The base resin of the thermoplastic resin compound used for the foam insulation of the electric wire of the present invention is not particularly limited as long as it is a thermoplastic resin. However, a thermoplastic fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP) ) And tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Properties suitable for foaming are preferably those having a melt index (MI, 190 ° C., 2.16 Kgf) measured according to ASDTM-D1238-70 of 14-30 g / 10 min. In the case of these FEPs and PFAs, the usual ones have a problem in terms of dielectric properties due to the presence of terminal functional groups, and thus preferably stabilized by subjecting the terminal functional groups to fluorination treatment or the like. Use is desirable. As a commercial product of FEP subjected to such fluorination treatment, 5100J (trade name, MI = 22) manufactured by Mitsui DuPont Fluorochemical Co., Ltd., and as a commercial product of PFA, 440HP-J manufactured by Mitsui DuPont Fluorochemical Co., Ltd. (Product name, MI = 15).

  As the porous body of the foam nucleating agent added to these base resins, zeolite, silica, activated carbon, silica gel or the like can be used. When used as an insulator for electric wires, the size (particle diameter) of these porous bodies is 1 to 10 μm, preferably 1 to 5 μm in median diameter (d50). The reason is that, when the submicron is less than 1 μm, secondary aggregation occurs and the number of particles that substantially contribute to foaming is reduced, so that finer foaming cannot be obtained. On the other hand, if the thickness exceeds 10 μm, the number of particles contributing to foaming in the unit volume decreases as in the case of secondary aggregation, and it is impossible to obtain finer foaming. And although it also depends on the specific surface area of the foam nucleating agent, the amount added to the base resin is preferably 0.1 to 1.5% by mass. Particularly in the case of zeolite, the median diameter is preferably 1 to 10 μm and 0.1 to 1.0% by mass. In the case of silica, the median diameter is preferably 1 to 10 μm and 0.1 to 1.5% by mass.

  The base resin to which the porous body is added is mixed as a thermoplastic resin compound before extrusion. At that time, if the drying is insufficient, in particular, moisture remains attached to the porous body. If it exists, as will become clear from the test described later, the foamed cell diameter cannot be reduced. Of course, the function of the porous body, that is, the adsorption action of the foaming gas such as nitrogen gas or carbon dioxide gas is also lowered. In addition, since the adsorbed moisture evaporates at the time of foaming and promotes the foaming action, the foam control itself becomes difficult. If moisture evaporates, it becomes difficult to control the gas pressure for injecting the foaming gas. As a result, a large variation in the degree of foaming occurs. Furthermore, since moisture adsorption varies depending on the season and date, it is difficult to secure a stable foaming degree in this respect as well. Furthermore, in the electric wire, when moisture remains in the insulator, it may cause various specific deteriorations. For these reasons, the present invention requires that the thermoplastic resin compound be sufficiently dried before extrusion and supplied to the extruder side in this dried state.

  For the thermoplastic resin compound to which such a porous body is added, if necessary, other additives such as antioxidants, copper damage inhibitors, flame retardants, dispersants, inorganic fillers, crosslinking agents, A crosslinking aid or the like can be appropriately added.

  FIG. 1 shows an example of a foam insulated wire obtained by the method for producing a foam insulated wire according to the present invention. This foam insulated wire is a foam coaxial cable. In the figure, 1 is an internal conductor such as a stranded wire conductor, 2 is a foam insulator in which the thermoplastic resin compound of the present invention is coated on the conductor 1 by extrusion molding. 3 is a metal layer (outer conductor) made of metal braid or corrugated copper pipe, 4 is a sheath made of polyethylene or the like, 5a and 5b are an inner skin layer and an outer skin layer with a thickness of about 50 μm, if necessary. is there. The outer diameter of the cable is not particularly limited, but is formed as about 3 to 50 mm. In addition, an aluminum tape etc. can also be put between the insulator 2 and the metal layer 3 as needed.

  FIG. 2 shows an example of an extrusion apparatus system for carrying out the method for manufacturing a foam insulated wire according to the present invention. 10 is a first extruder, 11 is a hopper (resin supply port) with a drying unit (dryer) of the first extruder 10, 12 is a built-in drying unit such as a heater of the hopper 11, and 13 is a thermoplastic in a dry state An external storage unit (external hopper) in which a resin compound is stored, preferably provided with a drying means such as vacuum drying, and 14 is a compound transport pipeline connected from the external storage unit 13 to the hopper 11 of the first extruder 10. It is. The space between the external reservoir 13, the compound transport pipe 14 and the hopper 11 with the drying unit of the first extruder 10 is maintained in an airtight state. That is, the thermoplastic resin compound supplied to the external storage unit 13 in a dry state is supplied to the hopper 11 with a drying unit of the first extruder 10 while maintaining the dry state.

  Reference numeral 15 denotes a gas injection unit of the first extruder 10, and 20 denotes a gas pressure control means of the first extruder 10, which includes an air compressor 21 and a gas booster 22 having a built-in buffer tank. Reference numeral 30 denotes a gas cylinder (for example, two) filled with a foaming gas such as nitrogen gas or carbon dioxide gas. Here, the original pressure of the foaming gas supplied from the gas cylinder 30 is increased to several times the operating pressure by the gas booster 22 and led to the built-in buffer tank, and the operating pressure is the gas injection section 15 of the first extruder 10. So that it can be injected stably. Thereby, the stable gas supply which suppressed the fluctuation | variation of gas pressure is obtained.

  40 is a second extruder for forming an outer skin layer, 41 is a crosshead of the second extruder 40, 50 is a third extruder for forming an inner skin layer, 51 is a crosshead of the third extruder 50, and 60 is 61 is a conductor feeding section, 62 is a tension adjusting dancer, 63 and 64 are preheating sections, a cooling section such as a 65 water tank, 66 is a winding capstan, and 67 is a tension adjusting section. A dancer 68 is a winding part for an electric wire (intermediate electric wire product). Here, after the outer skin layer is formed, it is once wound up as an electric wire intermediate product. However, the outer skin layer can be continuously covered with a metal layer (outer conductor) and a sheath without being wound up.

  In order to produce a foam insulated wire by the extruder system configured as described above, first, the base resin and the porous body are kneaded with another extruder to obtain a thermoplastic resin compound, and as described above, the external storage When a drying means such as vacuum drying is attached to the unit 13, heating is performed at about 80 ° C. and vacuum drying is performed to remove unnecessary gas, particularly moisture.

  Then, the dried thermoplastic resin compound is sent to the hopper 11 of the first extruder 10. The hopper 11 is also continuously dried by the attached drying unit 12 so that unnecessary moisture is prevented from being mixed as much as possible.

  From this state, the first extruder 10 is driven, and the foaming gas is supplied from the gas cylinder 30 to the gas booster 22 side, and the gas booster 22 and the air compressor 21 are controlled to supply the foaming gas to the first extruder. 10 gas injection portions 15 are injected. On the other hand, if the electric wire running line 60 is also driven and the conductor is fed out, the desired inner skin layer 5a, foamed insulator 2 and outer skin layer 5b can be sequentially coated. Since the inner skin layer 5a is also provided, the adhesion between the inner conductor 1 and the foamed insulator 2 is improved, so that the pull-out force of the insulator can be improved. When the outer skin layer 5b is provided, unevenness in appearance can be suppressed, VSWR (Voltage Standing Wave Ratio) can be improved, and a function of preventing degassing can be obtained, so that foam control is facilitated. In addition, as each of these skin layer materials, polyethylene (for example, low density polyethylene) is usually used. If the layer thickness is too thick, the foaming degree of the entire foamed insulator may be lowered. (Coating) itself is difficult, so about 50 μm is preferable. Any one of these skin layers may be provided, and in addition to coextrusion with the foamed insulator, each may be extruded alone.

  When it is based on the manufacturing method of the foam insulated wire which concerns on this invention, it is not limited to the said foamed coaxial cable, A normal foam insulated wire can be manufactured.

<Examples and comparative examples>
First, using the thermoplastic resin compounds (Examples 1 to 32 and Comparative Examples 1 to 14) having the compositions shown in Tables 1 to 5, a foamed coaxial cable of each sample having substantially the same structure as FIG. 1 is manufactured. did. In the production of each sample cable, an extrusion apparatus system shown in FIG. 2 was used. Here, the outer diameter of the inner conductor is 0.9 mm, the outer diameter of the foamed insulator is 2.3 to 2.4 mm, and the outer diameter of the entire cable is 3.0 mm. More specifically, after covering the foamed insulator by gas foaming with nitrogen gas, a corrugated outer conductor and a sheath such as polyolefin or PVC were applied. As the insulator material, an inner skin layer of FEP or PFA was provided on the outer periphery of the inner conductor, and an outer skin layer of FEP or PFA was provided on the outer periphery of the foamed insulator. In addition, when drying the thermoplastic resin compound, as described above, it was heated to about 80 ° C. and vacuum-dried by the drying means of the external storage unit.

Further, the thermoplastic resin which is the base resin used is a tetrafluoroethylene-hexafluoropropylene copolymer (FEP, 5100J (trade name), MI = 22, manufactured by Mitsui Dupont Fluoro Chemical Co., Ltd.), a thermoplastic fluorine-based resin. It is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer [PFA, 440HP-J (trade name, MI = 15), manufactured by Mitsui Dupont Chemical Co., Ltd.]. It is the zeolite (median diameter 1-10 micrometers, Showa Kasei Co., Ltd.) and the silica (median diameter 1-10 micrometers, Showa Kasei Co., Ltd.) of the porous body used.
The sample cable of Comparative Example 13 does not use the gas pressure control means, that is, the gas booster with a built-in buffer tank. In Comparative Example 14, the non-dried thermoplastic resin compound is supplied to the first extruder. is there. Moreover, the numerical value of a compounding material represents the mass%.

  About each sample cable, the characteristic test shown in Table 1-Table 6 is performed, and the characteristic [foaming degree, foam thickness, average foam cell diameter (average, standard deviation), appearance (surface roughness), outer diameter fluctuation range] Asked.

<Foaming degree test>
The foam insulation of the sample cable was taken out, and the foaming degree was determined by the formula: foaming degree = (1-specific gravity after foaming / specific gravity before foaming) × 100. Here, the degree of foaming is about 50%.

<Foam thickness test>
The foam insulation of the sample cable was taken out and measured directly. Each sample has a thickness of about 700 μm.

<Foamed cell diameter test>
A cross section of the foam insulation of the sample cable was photographed and observed with a scanning electron microscope (SEM), the foam cell was recognized by a computer program, and the average foam cell diameter (μm) was obtained by statistical data processing. Deviations were also determined.

<Appearance test>
The appearance of the sample cable was visually observed, and “good” was displayed when there was almost no unevenness (surface roughness) on the surface, and “bad” was displayed when there were many irregularities on the surface.

<Outer diameter fluctuation range test>
The external appearance of the sample cable was imaged and observed by SEM, and the outer diameter fluctuation width (μm) of the surface was obtained by image processing.

  As apparent from Tables 1 to 5 above, in the case of the foamed coaxial cable of the present invention (Examples 1 to 32), it can be seen that all the characteristics are good. In particular, it can be seen that the foamed cell diameter is less than 140 μm (average) at a foaming degree of 50%. In other words, this is less than about 1/5 of the thickness of the foamed insulator (around 700 μm), and it can be seen that finer foaming is obtained.

On the other hand, in the case of the foamed coaxial cable lacking the conditions of the present invention (Comparative Examples 1 to 14), it can be seen that there is a problem in any point.
That is, Comparative Examples 1, 3, 5, and 7 are cases where the amount of the porous material added is less than the requirement of the present invention, the foamed cell diameter is 140 μm (average) or more, the appearance is poor (surface roughness), and the outer diameter fluctuation range. Can be seen to be large. On the other hand, Comparative Examples 2, 4, 6, and 8 are cases where the amount of the porous material added is larger than the requirements of the present invention, and although the foamed cell diameter, appearance, and outer diameter fluctuation range are equivalent to the present invention, It can be seen that the effect of improving the cracking rate is small, resulting in an increase in cost, and there is a concern that the electrical characteristics may be lowered due to the increase in the amount.

  In Comparative Examples 9 and 11, the addition amount is 0.5% by mass that satisfies the requirements of the present invention, but when the particle size is smaller than the requirements of the present invention (0.5 μm), the foamed cell diameter is not so large. It can be seen that the foam cell distribution (standard deviation) is widened, and finally it has a large outer diameter variation. This is presumed that when the particle size is about 0.5 μm, the foamed cells generated by the secondary aggregation are combined to form open cells. On the other hand, in Comparative Examples 10 and 12, the addition amount is 0.5% by mass that satisfies the requirements of the present invention, but when the particle size is larger than the requirements of the present invention (20 μm), it can be seen that the cells become huge foam cells. . This is presumed that the number of particles per unit volume decreases depending on the size of the particle size, so that the foaming gas concentrates in one foam cell and develops into a huge foam cell. That is, it is necessary to pay sufficient attention to the particle size of the porous body.

  Comparative Example 13 is a case where there is no gas booster with a built-in buffer tank. For this reason, there is a fluctuation in the foaming gas pressure (17 to 18.5 MPa), and as a result, it can be seen that both the foamed cell density and the cell diameter fluctuate in the longitudinal direction, resulting in a large outer diameter fluctuation range. Comparative Example 14 is a case where the resin compound was not dried. There is a possibility that the moisture adsorbed on the porous body evaporates and becomes excessively foamed. For this reason, in order to suppress foaming, the foaming gas pressure was kept low (13 MPa), and foaming was performed. The foaming fluctuated. As a result, it can be seen that the outer diameter fluctuation range becomes large due to poor appearance. If there is residual moisture, there is a concern that foam control is greatly influenced by the season and date. For this reason, the drying treatment of the resin compound is an essential condition in the present invention.

It is the vertical end view which showed an example of the foam insulated wire obtained by the manufacturing method of the foam insulated wire which concerns on this invention. It is the schematic explanatory drawing which showed an example of the extrusion apparatus system for enforcing the manufacturing method of the foam insulated wire which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal conductor, 2 ... Foam insulator, 3 ... Metal layer (outer conductor), 4 ... Sheath, 5a ... Inner skin layer, 5b ... Outer skin layer, 10 * .... First extruder, 11 ... Hopper (resin supply port) of the first extruder, 12 ... Drying part of the hopper, 13 ... External storage part (external hopper), 14 ... Compound transportation Pipe line, 20 ... gas pressure control means, 21 ... air compressor, 22 ... gas booster, 30 ... gas cylinder, 40 ... second extruder, 50 ... third extruder , 60 ... Electric wire running line

Claims (8)

A thermoplastic resin compound added with a porous material as a foam nucleating agent is supplied in a dry state to an extruder, and a foaming gas is continuously injected into the extruder by a gas injection unit equipped with a gas pressure control means. A method for producing a foam insulated wire, characterized by extruding a foam insulation outward of a conductor. The base resin of the thermoplastic resin compound is a thermoplastic fluororesin such as a tetrafluoroethylene-hexafluoropropylene copolymer or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. Manufacturing method for foam insulated wires. The method for producing a foam insulated wire according to claim 1 or 2, wherein the porous body is zeolite, silica, activated carbon, or silica gel. 3. The foam insulated wire according to claim 1, wherein the porous body is zeolite having a median diameter of 1 to 10 μm and is added in an amount of 0.1 to 1 mass% with respect to a base resin of the thermoplastic resin compound. Production method. 3. The foam insulation according to claim 1, wherein the porous body is silica having a median diameter of 1 to 10 [mu] m and is added in an amount of 0.2 to 1.5% by mass based on the base resin of the thermoplastic resin compound. Electric wire manufacturing method. An external storage part in which the thermoplastic resin compound in the dry state is stored, a compound transport pipeline connected from the external storage part to the hopper of the extruder and an hopper of the extruder are in an airtight state, and the dry state 6. The method for producing a foam insulated wire according to claim 1, wherein the thermoplastic resin compound is supplied to an extruder. The method for producing a foam insulated wire according to claim 1, wherein the hopper of the extruder is a hopper with a drying section. 8. The production of a foam insulated wire according to claim 1, wherein the gas pressure control means of the gas injection part comprises an air compressor and a gas booster with a built-in buffer tank. Method.

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